STScI Preprint #1335

HST Observations of Superluminal Motion in the M87 Jet

We present observations of the M87 jet made with the Faint Object Camera on board HST at five epochs between 1994 and 1998. These observations reveal ten superluminal features within the first 6" of the jet, with eight of these having apparent speeds in the range 4c to 6c. Two additional features within the first arcsecond of the jet have subluminal speeds of 0.63c and 0.84c. The latter of these, named HST-1 East, appears to emit new superluminal features moving at 6c which subsequently fade with a half-intensity timescale of ~ 2 years. The fastest speeds we observe require Lorentz factor 6 for the bulk flow, and a jet orientation within 19 degrees of the line-of-sight, in the context of the relativistic jet model. Finding such large in an FR-I radio source like M87 strongly supports BL Lac/FR-I unification models. These large speeds help to mitigate the particle lifetime problem posed by the optical emission, as well as the jet confinement problem.

Status:

Appeared in: The Astrophysical Journal

Affiliations:

Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, 21218